Casing for a wellbore that has just been drilled is assembled at the surface as joints are added and the string is lowered into the wellbore. As the joints are added at the surface on the rig floor, it is desirable to fill the casing. Filling the casing before it is run into the wellbore prevents pressure imbalances on the casing as it is being advanced into the wellbore. Additionally, once the casing is filled, it may be desirable to circulate through the casing as it is being run into the wellbore. It may also be desirable to rotate the casing as it is being advanced into the wellbore. Prior devices have been developed to fill the casing and to circulate it. These devices used in the past are illustrated in U.S. Pat. Nos. 4,997,042 and 5,191,939. These devices illustrated in these patents employed an inflatable element which would seat against the inside of the casing, followed by a mechanical setdown force which opened ports to allow for circulation. Filling in this device was accomplished by displacement of a valve member past a lateral port to expose the lateral port to allow the casing to fill. One of the problems with the prior designs is that excessive erosion occurred at the valve member used for filling the casing, undermining its reliability. Additionally, the inflatable member used to isolate the top of the casing for the purposes of circulation also required maintenance. In order to circulate with the prior designs, not only did an inflatable have to get a good sealing grip on the inside of the casing, but also the circulating ports had to be mechanically exposed using setdown weight. The configuration and nature of the operation of these prior designs made them prone to erosion. Additionally, there were complexities in the normal operations of such designs which required the dropping of balls in order to activate a valve member for filling, as well as the use of an inflatable for sealing.
Accordingly, it is an object of the present invention to provide a system that simplifies the construction of the apparatus useful for filling and circulating casing. The fill valve has been designed to minimize erosive effects and simplify the operation. Another object of the apparatus is to eliminate the use of inflatables to simplify the design and the cost of constructing the apparatus. Accordingly, alternatives to inflatables, such as cup seals, have been employed. Finally, to facilitate the operation of the apparatus, the circulation valve has been configured to easily open fully, while at the same time allowing the fill valve to close so that the fill valve does not encounter the erosive effects of flow during circulation. In a further effort to streamline the design, another objective has been to provide an apparatus with an appropriate control so that a singular valve can provide a dual function of filling and circulating. These and other objectives accomplished by the apparatus will become more apparent from a review of the detailed description below.